Aliphatic and aromatic polyamines have been used in the past for curing epoxy resins. It is well known that the aliphatic amines react at a faster rate with epoxy resins than do aromatic polyamines. Aliphatic polyamines can effect cure at room temperature while aromatic polyamines generally require more rigorous cure conditions or additives which act as accelerators.
Representative patents which describe epoxy resins and the utilization of aromatic and cycloaliphatic amines as curatives, therefore including representative hydrogenation processes are as follows:
U.S. Pat. No. 2,817,644 discloses a process for curing and resinifying polyepoxides by reacting the polyepoxides with hydrogenated aromatic primary or secondary amines. Examples of aromatic amines which could be hydrogenated to form the cycloaliphatic counterparts include p,p′-methylenedianiline, 2,4-diaminotoluene, and the like. The hydrogenated aromatic amines provide epoxy resin products having excellent hardness and excellent resistance to solvents and water.
U.S. Pat. No. 2,981,711 discloses the use of amines as hardening agents for epoxy resins formed by the reaction of a polyglycidylether of a polyhydric phenol with epichlorohydrin. Both aromatic and cycloaliphatic amines are represented and these include para, para′-diaminodiphenylmethane, para, para′-diaminodiphenylpropane, and cycloaliphatic amines include diaminodicyclohexylmethane (often referred to as PACM), diaminodicyclohexylpropane and diaminotricyclohexylmethane.
U.S. Pat. No. 3,959,374 describes a process for the catalytic hydrogenation of methylene-bridged polyphenylamines which contain trace impurities and oligomers. More specifically a crude methylenedianiline feed containing these impurities and oligomers is initially treated with hydrogen in the presence of a nickel containing hydrogenation catalyst prior to hydrogenation in the presence of a ruthenium catalyst. The pretreatment overcomes low yields (52.4%) and long reaction times associated with nickel and cobalt. In the absence of the pretreatment, ruthenium catalysts, although commonly used for hydrogenation of purified methylenedianiline, are not suited for hydrogenation of a methylene dianiline feed containing impurities, e.g., isomeric impurities.
U.S. Pat. No. 4,226,737 and 4,321,353 disclose epoxy curatives which are methylene-bridged polycycloaliphatic polyamines represented by the structural formulas: wherein x and y are from 0-2 and the sum of x plus y is from 1 to 4. Typically, the curative consists essentially of from 50 to 75% of the methylene-bridged tricyclohexyltriamine and from 15 to 30% of the tetracyclohexyltetramine. The patentees report that the curing agents overcome substantial problems encountered with prior art amine curatives in that they have lower volatility and reduced toxicological properties. In addition, the patentees report higher glass transition temperatures, and thus improved thermal properties, can be achieved vis-à-vis 1,2-cyclohexanediamine.
U.S. Pat. No. 5,280,091 teaches the partial hydrogenation of three and four ring oligomer condensation products of formaldehyde and aniline or toluidine forms a mixture of methylene bridged poly(cycloaliphatic-aromatic)amines (sometimes referred to as “MPCA”) represented by the formula: wherein R is hydrogen or methyl, x is 1-3, y is 0-2 and the sum of x and y is from 2 to 4. The hydrogenated product is purified by distillation and used as a curing agent to produce epoxide resins having excellent gloss and water spotting resistance, low toxicity, excellent thermal properties, chemical resistance, and mechanical properties.
British Patent 1,536,808 discloses a process for the hydrogenation of methylene bridged aromatic amines, such as, methylenedianiline (MDA). The patentees suggest that it is well known that the mixed isomeric methylene bridged polycyclohexylpolyamines are useful as curing agents for vicinal epoxides.